Method and system for forming RF reflective pathways

ABSTRACT

The present invention provides for a system and two methods for forming RF reflective pathways. These pathways can form a radio frequency identification tag. A first method uses a thermal transfer ribbon, coated with a conductive material that is engaged with a receiver substrate. A thermal print head will heat a composition on the thermal transfer ribbon in order to transfer it to the receiver substrate. This transfer composition forms the RF reflective pathway. In an alternative method, a receiver substrate is heated in order to react conductive material thereon. This receiver substrate is also heated by a thermal print head to form a RF reflective pathway.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of co-pending application Ser. No.09/880,001, filed on Jun. 14, 2001, which is a Continuation-in-Part ofapplication Ser. No. 09/839,126, filed on Apr. 23, 2001. Thisapplication also claims priority under § 119(e) of application Ser. No.60/295,580 filed on Jun. 5, 2001. The entire contents of all of theaforementioned applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system and method for forming RFreflective pathways. In particular, the system and method is for makingvariably printed radio frequency antennas for radio frequency tags.

2. Description of the Background Art

Various printing arrangements for forming antennas are known. However,variable demand printing for forming electrically conductive pathways orantennas is not known.

One known method is from U.S. Pat. No. 4,265,703 to Terliska, the entirecontents of which are hereby incorporated by reference. In this patent,a method of preparing a fibrous structure containing metallic fibers isdisclosed. Other patents to Greene, U.S. Pat. No. 5,204,681, 5,291,205and 5,581,257 disclose different radio frequency automaticidentification systems. These patents try to detect small resonatingparticles using an interrogating RF signal.

A resonating pattern can be chosen for an item to be labeled. Thispattern can be a designation for the item such as a barcode or it can bea random pattern which is to be assigned to a database for laterconfirmation. In a barcode situation, each barcode is associated with aparticular product. Likewise, a resonating pattern can be chosenaccording to the product being labeled. In this case, an identificationtag may be created which has a random but known response associated withit so that future scanning of that pattern can be associated with theitem labeled. Advantages of using a resonating pattern system overcurrent, widely used barcode system is the ability to read in non-lineof sight situations, the ability to read through dirt, soiling, etc. onthe surface and the possibility of extending automation by not requiringhuman alignment of the reading system.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amethod and system to produce variable on-demand printing of radiofrequency reflective (hereinafter RF reflective) pathways. Such pathwayscan be used to form antennas for radio frequency tags. Two differentmethods can be utilized for forming such conductive pathways.

In one of these methods, the following steps are carried out: providinga thermal transfer ribbon, moving the thermal transfer ribbon past aheat source, engaging the thermal transfer ribbon with a receiversubstrate as the thermal transfer ribbon moves past the heat source,selectively heating portions of the thermal transfer ribbon with theheat source, and transferring a composition from the thermal transferribbon to the receiver substrate, the selective heating enabling adesired pattern of the composition to be transferred to the receiversubstrate, the composition including a RF reflective material.

In another method for forming RF reflective pathways, the followingsteps are carried out: providing a substrate coated with reactivematerial, moving the substrate past a heat source, selectively heatingportions of the substrate with the heat source, and developing thereactive material on the substrate during exposure to heat from the heatsource to develop a desired pattern on the substrate, the reactivematerial becoming a RF reflective material.

Further, it is an object of the present invention to also provide asystem for producing radio frequency tags comprising a conveyor formoving a substrate, a thermal print head, the conveyor moving thesubstrate past the thermal print head, the thermal print head beingselectively actuatable to heat a desired pattern on the substrate, meanson the substrate for reacting with the heat source to form RF reflectivepathways, the means including a heat sensitive composition on thesubstrate.

Further scope of the applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a schematic side view of a first system for forming RFreflective pathways of the present invention; and

FIG. 2 is a schematic side view of a second system for forming RFreflective pathways of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring in detail to the drawings and with particular reference toFIG. 1, a first system 10 for forming RF reflective pathways is shown.While the specification will discuss RF reflective pathways, it shouldbe noted that these pathways will also be electrically conductive. Thissystem 10 includes a conveyor 12 for infeeding a thermal transfer ribbon14 and a received substrate 16. This conveyor 12 is only schematicallyshown in FIG. 1 as a pair of feed rolls. It should be appreciated thatany type of conveyor system could be utilized. For example, a beltconveyor, chain conveyor, series of rollers, or any other known conveyorsystem could be used. Moreover, while only a pair of rollers 12 areshown, it should be contemplated that a continuous conveyor can be usedover the length of the system 10 or any suitable number of conveyorunits can be incorporated into the conveyor system.

The thermal transfer ribbon 14 and receiver substrate 16 are fed past aheat source or thermal print head 18. The thermal print head 18 willselectively heat portions of the thermal transfer ribbon 14 toultimately form a desired pattern on the receiver 16, as will bediscussed below. While such a thermal print head 18 is known, its use ina method for forming RF reflective pathways is new. In addition, abacking roller 20 is provided to support the thermal transfer ribbon 14and receiver substrate 16. While a backing roller 20 is shown, it shouldbe noted that other support surfaces could be used. For example, a flatsupporting table or other structure could be opposed to the print head18.

The thermal transfer ribbon 14 has a reactive coating or a conductivetransferable material thereon. When this reactive coating or material isheated by the thermal print head 18, a RF reflective pathway can beprinted on the receiver substrate 16. Thermal transfer ribbon 14 eitherhas a conductive material or RF reflective material or a material thatbecomes conductive or RF reflective upon the application of heat. Theheat from print head 18 will serve to transfer the material to receiversubstrate 16 and in some instances will also serve to activate thematerial to make it conductive or RF reflective. In those circumstances,the transferred composition will be a RF reflective precursor.

The use of this print head 18 allows printing of a pathway in any shape,length, or size onto the receiver substrate 16. Thus, great flexibilityis had with the use of the thermal print head 18. The RF reflectivepathway 26 is schematically shown in FIG. 1. While a generallyrectangular pathway is shown, it is important to note that the length,width, shape and size of the pathway can easily be varied by using printhead 18. The conveyor 12 will enable on-the-fly printing of pathways 26.Of course, batch processing is also possible. In such an arrangement, acontinuous transfer ribbon and receiver substrate can be incrementallyfed past the print head 18 or discrete portions of a ribbon 14 andsubstrate 16 could be used. For example, a feeder conveyor could moverectangular overlaying sheets of transfer ribbon and substrate throughthe system 10 past the print head 18.

The thermal transfer ribbon 14 is brought into engagement with thereceiver substrate 16. This engagement, along with the heating of thethermal transfer ribbon 14 by the thermal print head 18, will causetransfer of a composition from the ribbon 14 to the receiver substrate16. Thus, a complicated arrangement using magnets, as taught in U.S.Pat. No. 5,061,093 to Yamaguchi et al. for example, is not needed.

The thermal transfer ribbon 14 is coated with the composition. Thetransfer ribbon is made up of a transfer substrate which can be madefrom a polymeric film or paper. Suitable transfer substrate materialsinclude, but are not limited to, paper, polyester, polyethylenenaphthalate, polyamide, polyolefin, cellulose and polycarbonate. Onepreferred transfer substrate is polyester film, manufactured by Dupont™under the Mylar™ brand name. Generally, Mylar™ is a polyester flexiblefilm. Important properties of the transfer substrate include hightensile strength, thin thickness and low heat resistance.

The transfer substrate of the thermal transfer ribbon is coated with aconductive composition that is designed to be transferred to thereceived substrate 16 using the thermal print head 18. This coating iscomprised of a conductive material, wax, binders, surfactants,dispersants and other additives. The primary component of the transferlayer is the RF reflective material. The material may be comprised ofmetallic inks, metallic substances, metallic dispersions, metallicsalts, carbon based inks, or other conductive substances, etc. Apreferred metallic substance is manufactured by Parelec™ under theParamod™ brand name. Generally, the higher the conductivity or RFreflectance of the conductive material, the better.

The transfer coating for the thermal transfer ribbon 14 also contains awax as another main component. The wax is designed to melt or softenunder the heat supplied by the thermal print head 18. This will aid inthe transfer of the coating layer to the receiver substrate 16. Examplesof suitable waxes are carnuaba wax, paraffin wax, low molecular weightpolyethylene wax, etc.

Binders are also included in the thermal transfer ribbon 14. Thesebinders in the coating layer aid in cohesion of the coating and providetack properties for adhesion to the receiver substrate 16. Examples ofsuitable binders are styrene copolymers, polyethylene resin,polystyrene, vinyl chloride polymers, vinyl acetate polymers, etc.Surfactants, dispersant and other additives are incorporated as neededfor proper processing, coating and to aid in the transfer properties.

The transfer coating layer can be applied to the transfer ribbonsubstrate using a Meyer rod, airknife, roll coater, blade or anysuitable coating method. The coat weight applied is in the range 1.5g/m² to 30 g/m².

The coated transfer ribbon can then be used with the thermal print head18 and a thermal printer to create any size, shape, length, etc. a radiofrequency identification tag. The conductive material is transferredonto the receiver sheet 16. This receiver sheet is a substantiallynon-conductive substrate such as paper, plastic film and the like.Alternatively, the sheet can be a conductive substrate that has beencoated with an electrical insulating layer.

Turning now to FIG. 2, a second method and system 10′ for forming RFreflective pathways will be described. These pathways can also be usedfor antennas in radio frequency tags, similarly to that described inFIG. 1. Many of the components and alternative arrangements in thissecond system 10′ are the same as that in the first system, and theirdescription will not be repeated.

In the second system 10′, a thermal transfer ribbon 14 is not used.Rather, a second receiver substrate 16′ is utilized. This substrate usedcan be selected from paper, polymeric films, cellulose materials andother thin, flat substrates. This substrate is coated with a compositionthat is designed to react when exposed to heat generated from thethermal print head 18. This coating is comprised of a reactive materialforming an RF reflective material. This coating could include areducible metallic material, binders, fillers, surfactants, dispersants,and other additives.

The primary component of the coating layer is the reactive materialforming the RF reflective material such as a reducible metallicmaterial. This reducible material may be comprised of sorbitol copperformate, copper sulfate, cuprite, tenorite, silver nitrate, and thelike. The higher the conductivity of the reduced reducible material, thebetter.

Binders are included in the coating layer to aid in cohesion of thecoating while not inhibiting the conductivity of the reduced material.Examples of suitable binders are styrene butadiene copolymers, polyvinylalcohols, starch, vinyl chloride polymers, vinyl acetate polymers,methyl cellulose, etc. Surfactants, dispersants and other additives areincorporated as needed for proper processing, coating, and to aid in thetransfer properties. The coating layer can be applied to the substrateusing a Meyer rod, airknife, roll coater, blade or any other suitablecoating method. The coat weight applied is in the range of 1.5 g/m² to30 g/m².

With the present system, variable, on-demand printed RF reflectivepathways can be formed. The invention utilizes two methods for printingthe pathways, thermal transfer and direct thermal. The printed pathwaysare suitable for use as a radio frequency identification tag. With thefirst described thermal transfer method, a ribbon 14 coated with aconductive material is used that is transferred to another substrate 16upon application of heat by the thermal print head 18. In the directthermal method, a receiver substrate 16′ is used that has a conductivematerial which, when exposed to heat from a thermal print head 18, willform the pathways.

To summarize the steps of the first method of forming RF reflectivepathways, a thermal transfer ribbon 14 is provided. This thermaltransfer ribbon 14 is moved past a heat source or thermal print head 18by conveyor 12. The thermal transfer ribbon 14 is engaged with areceiver substrate as it moves past the heat source or thermal printhead 18. This thermal print head 18 will selectively heat portions ofthe thermal transfer ribbon 14, in order to transfer a composition tothe receiver substrate 16. This transferred composition forms a RFreflective pathway 26. The selective heating by the thermal print head18 enables a desired pattern of composition to be transferred to thereceiver substrate 16.

In the second method, a substrate 16′ is provided with a reactivematerial. This substrate 16′ is moved by conveyor 12 past a heat sourceor thermal print head 18. The heat source or thermal print head 18 canselectively heat portions of the substrate. This will develop thereactive material on the substrate 16′ to develop a desired pattern onthe substrate. This desired pattern will form the RF reflective pathway26.

With either method, a system 10 or 10′ can be used. The conductivecomposition on ribbon 14 or the reducible material on the secondreceiver substrate will act as means on the substrate for reacting toheat from the heat source or print head 18. The conductive compositionor reducible material is a heat sensitive composition on substrate 14 or16′.

The pattern of the RF reflective pathways, either developed in a desiredpattern on the substrate or transferred to the receiver substrate 16 cantake the pattern of a conventional bar code, for example of the typecomprising a plurality of spaced apart parallel vertical lines arrangedin a row.

The bar code of the above type, or bar code configured of other patternor standard, advantageously can be of multiple functionality, readableby either reflecting an RF signal or optically or infrared scannable, orall three.

The reactive material forming a RF reflective material can optionallyadditionally include some portion of dye precursors such as colorlesschromogenic materials and acidic developers. Developers can includephenolic reactive materials or near-IR phthalides such as taught byMathiaparanam in U.S. Pat. No. 5,157,012 or 5,086,171, said patentsincorporated herein by reference.

A variety of acidic developer materials are known for colorizingchromogenic materials. Acidic developer materials include: clays,treated clays (U.S. Pat. Nos. 3,622,364 and 3,753,761); aromaticcarboxylic acids such as salicyclic acid; derivatives of aromaticcarboxylic acids and metal salts thereof (U.S. Pat. No. 4,022,936).Various phenol based polymeric materials such as phenol-formaldehydepolymers: (U.S. Pat. Nos. 3,455,721, 3,244,550 and 4,573,063 and3,672,935) metal-modified phenolic resins (U.S. Pat. Nos. 3,732,120;3,737,410; 4,165,102; 4,165,103; 4,166,644 and 4,188,456; additionproducts of phenol and a diolefinic alkylated or alkenylated cyclichydrocarbon (U.S. Pat. No. 4,573,063), a glass comprising a biphenolcolor developer and a resinous material (U.S. Pat. No. 4,546,365) aphenol-aldehyde polymeric material (U.S. Pat. No. 3,672,935), oilsoluble metal salts of phenol-aldehyde novolak resins such as the zincsalt of p-octylphenol formaldehyde (U.S. Pat. No. 3,732,120; or, oilsoluble water insoluble metal salts such as zinc hexonate and an oilsoluble phenol-aldehyde novalak resin (U.S. Pat. No. 3,723,156).

Chromogenic materials include compounds such as the phthalide,leucauramine and fluoran compounds, which are well known color-formingcompounds. Examples of chromogenic materials include Crystal VioletLactone (3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophthalide, U.S.Pat. No. RE. 23,024)3,3-bis(4-diethylaminophenyl)-6-dimethylaminophthalide; phenyl-, indol-,pyrrol-, and carbazol-substituted phthalides (form example, in U.S. Pat.Nos. 3,491,111; 3,491,112; 3,491,116; 3,509,174); nitro-, amino-,amido-, sulfonamido-, aminobenzylidene-, halo-, anilino-substitutedfluorans (for example, in U.S. Pat. Nos. 3,624,107; 3,627,787;3,641,011; 3,642,828; 3,681,390); spirodipyrans (U.S. Pat. No.3,971,808); and pyridine and pyrazine compounds (for example, in U.S.Pat. Nos. 3,775,424 and 3,853,869. Other chromogenic compounds include:3-diethylamino-6-methyl-7-anilino-flouran (U.S. Pat. No. 3,681,390);2-anilino-3-methyl-6-dibutylamino-fluoran (U.S. Pat. No. 4,510,513) alsoknown as 3-dibutylamino-6-methyl-7-anilino-fluoran; 3-dibutylamino-7(2-chloroanilino) fluoran;3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-3,5′,6 tris(dimethylamino) spiro [9H-fluorene-9,1′(3′H)-isobenzofuran]-3′-one;7-(1-ethyl-2-methylindol-3-yl)-7-(4-diethylamino-2-ethoxyphenyl)-5,7,-dihydrofuro[3,4-b]pyridin-5-one(U.S. Pat. No. 4,246,318; 3-diethylamino-7-(2-chloroanilino)fluoran(U.S. Pat. No. 3,920,510);3-(N-methylcyclohexylamino)-6-methyl-7-anilinofluoran (U.S. Pat. No.3,959,571);7-(1-octyl-2-methylindol-3-yl)-7-7(4-diethylamino-2-ethoxyphenyl)-5,7-dihydrofuro[3,4-b]p7ridin-5-one;3-diethylamino-7,8-benzofluoran;3,3-bis(1-ethyl-2-methylindol-3-yl)phthalide;3-diethylamino-7-dibenzylamino-2,2′-spiro-di-[2H-1-benzopyran] andmixtures of any of the foregoing.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A system for producing radio frequency tags comprising: a conveyorfor moving a substrate; a thermal print head, the conveyor moving thesubstrate past the thermal print head, the thermal print head beingselectively actuatable to heat a desired pattern on the substrate; meanson the substrate for reacting with the heat source to form RF reflectivepathways, the means including a heat sensitive composition on thesubstrate.
 2. The system for producing radio frequency tags as recitedin claim 1, wherein the substrate is a thermal transfer ribbon andwherein the conveyor further conveys a receiver substrate past the heatsource, the receiver substrate and the thermal transfer ribbon beingengaged at the thermal print head and the heat sensitive compositionbeing initially provided on the thermal transfer ribbon being heated inthe desired pattern by the thermal print head and thereafter beingtransferred to the receiver substrate, the heat sensitive compositionwhich is not heated by the thermal print head remaining on the thermaltransfer ribbon, the heat sensitive composition transferred to thereceiver substrate forming RF reflective pathways on the receiversubstrate.
 3. The system for producing radio frequency tags as recitedin claim 1, wherein the heat sensitive composition on the substrateincludes at least one of metallic inks, metallic substances, metallicsalts, metallic dispersions and carbon based inks.
 4. The system forproducing radio frequency tags as recited in claim 1, wherein the heatsensitive composition on the substrate is at least one of sorbitolcopper formate, copper sulfate, cuprite, tenorite and silver nitrate andwherein the thermal print head only reacts with the heat sensitivecomposition in the desired pattern to form the RF reflective pathwayswith the reacted heat sensitive composition while unreacted heatsensitive composition remains on the substrate.
 5. A radio frequency tagproduced according to a method of forming radio frequency tags,comprising the steps of: providing a thermal transfer ribbon; moving thethermal transfer ribbon past a heat source; engaging the thermaltransfer ribbon with a receiver substrate as the thermal transfer ribbonmoves past the heat source; selectively heating portions of the thermaltransfer ribbon with the heat source; and transferring a compositionfrom the thermal transfer ribbon to the receiver substrate, theselective heating enabling a desired resonating pattern of thecomposition to be transferred to the receiver substrate.
 6. A radiofrequency tag producing according to a method of forming radio frequencytags, comprising the steps of: providing a substrate coated withreactive material; moving the substrate past a heat source; selectivelyheating portions of the substrate with the heat source; and developingthe reactive material on the substrate during exposure to heat from theheat source to develop a desired resonating pattern on the substrate,the reactive material forming a RF reflective material.